This invention relates to a bearing assembly for a work implement of a construction machine.
A rotational member for a work implement on a construction machine that includes a bearing assembly. The bearing assembly can include a boss portion of a first member (hereinafter referred to as xe2x80x9cbossxe2x80x9d) that is positioned and pivotally connected by a pin. The pin is arranged between a pair of bracket portions of a bifurcated member. FIG. 7 shows an example of a work implement on a excavator. The work implement has a boom 11 that is pivoted vertically in the front portion of the body frame 4, an arm 13 that is articulately connected at the end portion thereof, and a bucket 15 that is pivotally connected to the arm 13. The connections between the pivoting members of the work implement are provided with a bearing assembly at each pin joint.
Japanese patent application 1995-354061, filed on Dec. 28, 1995 and assigned to Hitachi Construction Machinery shows a known bearing assembly. FIGS. 8 and 9 show a cross sectional view of the bearing assembly described in the above-mentioned Japanese application, which is seen along line Mxe2x80x94M in FIG. 7. As shown in FIG. 8, the arm 13 has a boss 13a at the end portion thereof. A pair of bushings 61, 61 are fixed on opposing sides of a bore defined within the boss 13a, so that a pin 27 can slide axially in the bore of the boss 13a. A pair of bosses 15b, 15b are formed on a pair of bifurcated flanges or a pair of brackets 15a, 15a, which are positioned on the opposing sides of the end portion of the bucket 15. The pin 27 is inserted through the bore defined within the brackets 15a, 15a and the bushing 61, 61.
In the description of the aforesaid Japanese application, it is explained that the use of a heavy lubricant will prevent the bushing 61 from overheating while sliding around the pin 27, when the bushing is subjected to a heavy radial load. The use of a heavy lubricant also prevents vibration and frictional wear. Sintered hard alloy metals or ceramics such as tungsten carbide and the like are disposed on both of the end surfaces 13b, 13b of the boss 13a, as well as the opposing inner surfaces 15c, 15c of the bosses 15b that extends inward towards the brackets 15a, 15a. The brackets 15a, 15a face the end surface 13b, 13b and form anti-wear layers 71 and 72 respectively. The Japanese patent application explains that the anti-wear layers 71 and 72 have a hardness equal to earth and sand, so that the bushing surfaces are difficult to scratch, when earth, sand and the like get between the sliding surfaces of the bushings 61, 61. The anti-wear layers prevent the deleterious scouring action of the sand on the sliding surfaces of the bushing flange, which would result in abrasive wear.
FIG. 9 shows also another embodiment of the above-mentioned Japanese application. In the drawing, both end surfaces 13b, 13b of the bosses 13a and opposing inner sides 15c, 15c of the bosses 15b, 15b, which extend inward toward the brackets 15a, 15a, define a pair of annular grooves 81, 82, where a pair of rings 83, 84 are respectively installed. The rings 83, 84 are fixed by a number of screws 85. A pair of anti-wear layers 86, 87, which are formed by a spray coating process with sintered hard alloy metal or ceramics such as tungsten carbide prior to its installation, are positioned on the facing sliding surfaces of the rings 83, 84.
The following are drawbacks associated with the conventional technology described in the above-referenced Japanese patent application.
(1) Since the anti-wear layers 71, 72 and 86, 87 are bonded directly to the sliding surface of the annular rings by the spray deposit of the sintered hard alloy metal such as tungsten carbide; they can be equal in hardness to earth and sand containing aluminum, silica, quartz and feldspar, but not significantly harder. This results in quick degradation of the anti-wear layers 71, 72. In addition, the anti-wear layer made by spray forming is extremely thin, ranging from tens to hundreds of microns, resulting in a relatively short wear life. Furthermore, when hard gravel and the like as small as several millimeters get into the space between the rings 83 and 84 and a strong force is being applied, impressions that are created by the gravel reach the base metals through the relatively thin anti-wear layers 71 and 72 or 86 and 87 disposed thereon. This can increase the possibility of cracks and peeling of the anti-wear layers starting from the impressed portions.
(2) When the anti-wear layers 71, 72 or 86, 87 are worn out and damaged as described in (1), it very difficult to repair these parts with this particular type of bearing assembly on site. This leads to poor machine maintenance.
(3) With this type of bearing assembly, the ring shaped members 83, 84 and the anti wear layers 86, 87 are fastened by a number of screws 85 to both end surfaces 13b, 13b of the boss 13a and the opposing inner sides 15c of the bracket bosses 15b (FIG. 9). The ring shaped members 83, 84 repeat a reverse turn with the bucket 15 pivoted about the pin 27 with respect to the arm 13. This causes the screws 85 to be repeatedly subjected to lateral forces in opposite directions, which reduces the tightening force or axial tension of the screws 85 and raises the possibility that screws will loosen and fall free whenever the rings 83, 84 are subject to an additional thrust force. Thus, the described bearing assembly can suffer from the drawback of poor durability.
The present invention is directed to overcoming the problems described above. It is the object of the present invention to provide a bearing assembly for a work implement on a construction machine that has a significant bearing performance, excellent durability, and easy maintenance.